1. Field of the Invention
This invention relates to the enantioselective borane reduction of prochiral ketones and to certain borane-containing compounds useful as catalysts for that purpose.
2. Prior Art
Recently there have been a number of reports describing research on the enantioselective reduction of prochiral ketones by a wide variety of reagents made by mixing aluminum or boron hydrides and various chiral diols or aminoalcohols. See, for example, J. W. ApSimon et al., Tetrahedron, 42, 5157-254 (1986). Among the most interesting enantioselective prochiral ketone reductions have been those reported by S. Itsuno and co-workers which employ borane in tetrahydrofuran (THF) and a chiral .beta.-amino alcohol, (S)-2-amino-3-methyl-1,1-diphenylbutan-1-ol and the corresponding derivative from (S)-leucine thus far being the most effective (ca. 95% e.e. of (R)-1-phenylethanol from acetophenone). See, for example, J. Chem. Soc. Chem. Commun., 315-7 (1981); J. Chem. Soc. Chem. Commun., 469-70 (1983); J. Org. Chem., 49, 555-7 (1984); J. Chem. Soc. Perkin Trans. I, 2039-44 (1985); J. Chem. Soc. Perkin Trans. I, 2615-9 (1985); Bull. Chem. Soc. Japan, 60, 395-6 (1987). The disclosures of these and other documents referred to in the specification of this application are incorporated herein by reference.